The invention will find widespread application in making sports racing skis, as well as skis for adults, juveniles and children.
Diverse service and application conditions impose certain requirements upon the design of skis, largely the ability to retain strength and high elasticity at a minimized weight. Mechanical characteristics responsible for high performance quality of a ski dictate extremely complicated construction of up-to-date skis involving the use of various types of material (plastics, special coatings). Wood is used for the purpose as a filler only.
A modern ski blank may be regarded as a multi-ply material built up of the following layers: a top layer establishing the outside ski surface; a reinforcing layer; a wedge; another reinforcing layer; and a bottom layer (bed) serving as an external sliding face of the ski.
The outside (top) surface of a ski serves not only as the carrier of advertising slogans but also as a preventer of wear, detrimental effect of water or mechanical damage by the points of ski poles or stones. In addition, the outside surface of a ski imparts solidity thereto and serves as its construction element.
It is acryl-butadiene-styrene mixtures suggested by the firm Isovolta-Isosport (Austria) that are gaining most extensive application nowadays as the materials forming the outside surfaces of skis.
According to the method proposed by the afore-mentioned firm, the pellets of the acryl-butadiene-styrene mixture, after having been softened at an elevated temperature, are subjected to extrusion to produce a web whose width may be equal to that of either of the outside surfaces (top or bottom) of the ski being manufactured, for instance, 900 mm. The thus-obtained web is suitable for prolonged storage after having been reeled up into rolls on special devices. The final operation of the ski making process, i.e., producing the outside surfaces of a ski, is carried out by applying to the ski blank first a layer of epoxy adhesive, then a web built up of a mixture of acryl-butadiene-styrene; after exposing the ski blank to the effect of elevated temperature and pressure one can obtain an adequately strong joint of the aforementioned ski components. Some other adhesive compositions may be used for bonding together the ski blank and web forming the outside surfaces of the ski. However, it is expedient in such cases to pretreat one of the surfaces to be bonded either chemically or electronically so as to expedite chemical softening of the material and to increase the degree of roughness of the surface to be bonded (cf., e.g., U.S. Pat. No. 4,077,652).
However, the known method discussed above fails to provide higher structural characteristics of the ski as a whole, while the outside surfaces of the ski are highly liable to attrition wear and vulnerable to mechanical damage.
Another method of processing the outside surfaces of a ski is known, wherein used as a material forming the outside surfaces of the ski are laminated plastics obtained by impregnating some fibrous materials, such as paper, with thermosetting synthetic resins, followed by exposing them to high-pressure moulding. The various properties of the resultant laminated plastics depend upon the type of resin used as an impregnant. For instance, U.S. Pat. No. 3,707,296 describes melamine (a combination of formaldehyde and phenolformaldehyde resins) as an impregnant. The laminated plastics with such an impregnant is produced at 130.degree. to 160.degree. C. and a pressure of about 5 to 10 MPa in special presses.
Finnish Pat. No. 58,438 describes the use of fibrous matter in the form of loose mechanically non-adhered particles impregnated with epoxy resins curable at elevated tempertures, as the material to form the outside surfaces of a ski.
U.S. Pat. No. 3,628,802 discloses a possibility of using polyester, epoxy and polyurethane resins or mixtures thereof as an impregnant.
Austrian Pat. No. 349,336 describes a laminated material used to establish the outside surfaces of a ski, said material being composed of a fibreglass-reinforced layer of epoxy resin and a plastic film mechanically adhered thereto, said fibreglass-reinforced layer of epoxy resin being obtained by impregnating the fibreglass material with epoxy resin in combination with an appropriate amount of a curing agent.
According to FRG Pat. No. 1,939,334 the laminated material serving further as the outside surfaces of a ski, is made of plastic sheets by applying a thermosetting adhesive thereto, followed by curing said adhesive at a pressure and elevated temperature. Used as said adhesive is a mixture of 1,2-polybutadiene, a peroxide polymerization initiator and a chain extender.
All the laminated plastics mentioned hereinabove are bonded together with the ski blank by epoxy adhesive at elevated temperature and pressure. Alongside with epoxy adhesive used as a bonding matter may be a curable condensation product of formaldehyde, urea or melamine, phenol, resorcinol obtained after evaporation of the solvent.
As can be evident from the above-discussed, the process for production of laminated plastics is rather complicated, being as a matter of fact an individual technological process. In addition, the resultant laminated plastics are unfit for immediate use in making the outside surfaces of skis.
Thus, for example, the laminated plastic material needs pretreatment, before being applied to a ski blank, of its surface either chemically or electronically to improve adhesion on the surface to be bonded.
Moreover, the laminated plastics need be cut in pieces of a required size corresponding to the side surface, sliding face and top surface of a ski before being applied to the ski blank, which also sophisticates the method of making the outside surfaces of a ski.
FRG Pat. No. 2,407,971 describes a method of making the outside surfaces of a ski, according to which a layer of a fibrous material, such as cellulose is applied to the sliding surface of the ski blank, whereupon liquid epoxy resin is sprayed from a jet onto the fibrous material layer in an amount required for said material to impregnate. Epoxy resin thus applied to the ski surface is cured concurrently with the binding the ski components together at elevated temperature and pressure in a special press.
However, the fact that uncured epoxy resin is used in the process of forming the outside surfaces of a ski is a negative factor for the attending personnel from the sanitary-hygienic viewpoint since liquid epoxy resin causes skin irritation which might develop eczema.
At present the best characteristics are displayed when testing the top outside surfaces of a ski, by the materials made on the base of phenolic resins. Unfortunately substitution of phenolformaldehyde resin for epoxy resins finds but restricted application due to high curing temperature of the former resin, whereas a maximum temperature allowed in making plastic skis lies within 110.degree. and 120.degree. C. With due regard to all as that discussed above, the following process techniques are suggested by the firm "Isovolta-Isosport-80" (Austria):
1. Impregnation of paper with a compound featuring high phenolic resin content.
2. Drying the impregnated paper till an incomplete curing of phenolic resin.
3. Three or four plies of the impregnated paper are pressed together in the corresponding multiplaten presses to a definite pressing program, complete curing of phenolic resin occurring concurrently.
4. One-sided sanding of three- or four-ply sheet materials and their cutting into desired sizes.
Further on, the thus-obtained material is bonded to the ski blank with expoxy adhesive. The thus-produced ski features high mechanical characteristics. However, the process techniques applied for ski production are rather sophisticated and cumbersome and, moreover, involve much cost.
Known heretofore is also the production of the outside surfaces of a ski (particulaly its sliding face) using a material based on high molecular-weight polyethylene. Use is also made of diverse materials based on polyester, epoxy, polyurethane and phenolic resins containing some reinforcers (cf. Finnish Pat. No. 58438). Used as reinforcing layers are, as a rule, fibreglass plastics that impart excellent load-resisting properties to the ski.
However, when making skis from the aforementioned materials, specific properties of the bonding materials are of special importance, that is, special adhesives are required. Dense materials are bonded together as a rule with solvent-free epoxy adhesives. FRG Pat. No. 2,647,405 describes the use of the condensation product of formaldehyde, urea or melamine, phenol and resorcinol obtained after evaporation of the solvent, for bonding the outside surfaces of a ski. The bonding occurs at the second stage after the surfaces being bonded together have been forced against each other and cured at high temperatures.
FRG Pat. No. 3,003,537 describes the use of a polyamide layer instead of an adhesive for bonding the top outside surfaces of a ski, since polyamide is liable to melt down at elevated temperatures and to bond the surfaces together. However, the ski formation techniques applied by the various manufacturers differ but negligibly: when assembling a ski the reinforcer material is coated by a layer of adhesive on both sides to obtain a combination material composed of the top surface, fibre-glass plastic, ski blank, fiber-glass plastic and sliding face and subject to pressure-moulding in a ski-producing press.
As is obvious from the above discussion, the processes for production of materials made use of in making the outside surfaces of a ski are rather sophisticated independent techniques, and the materials thus produced are subject to chemical or electronic treatment before use in order to improve adhesion on the surface to be bonded. Besides, laminated plastics should be cut to pieces of a required size to suit the ski side surface before assembling the ski.